dude if you would have read the lore which you probably didnt you would know that both sivir and riven used to be officers of the noxian army. Sivir quitted the noxian forces as protest again the noxian ionian war being a pointless bloodshed and riven exiled herself as protest to noxus cooperation with zaun and the use of unconventinal (chemical warfare) even at the cost of friendly fire. The both stay true to their noxian origin but critisize the noxus high command for their recent and apparently wrong choises.